A technology, in which two display panels overlap each other and an image is displayed on each display panel based on an input video signal, is conventionally proposed to improve contrast of a liquid crystal display device (for example, see WO 2007/040139). Specifically, for example, a color image is displayed on a front-side (observer-side) display panel in two display panels disposed back and forth, and a monochrome image is displayed on a rear-side (backlight-side) display panel, thereby improving contrast. In the above-described liquid crystal display device, filtering processing (extension filtering) of extending a high-luminance region of the monochrome image is performed such that a desired image is visually recognized without generating an image deviation even if a display screen is obliquely viewed. For example, in the extension filtering, processing of setting the maximum gray scale value in a filter size to a gray scale value of a pixel (target pixel) in a center of a pixel region is performed on all pixels of each frame using a 3-by-3 pixel region as a filter size.